Bai YuZuo, Chen Hui, Yuan Zheng Wei, Wang WeiLin
Department of Pediatric Surgery, The Second Affiliated Hospital, China Medical University, Shenyang, People's Republic of China.
J Pediatr Surg. 2004 Apr;39(4):587-90. doi: 10.1016/j.jpedsurg.2003.12.002.
The embryologic and pathologic aspect of anorectal malformation (ARM) remains poorly understood. There is no universally accepted theory to explain anorectal embryology and the abnormal development that produces ARM. The aim of this study was to observe the developmental processes of anorectum in rats and to explore the abnormal embryonic development that leads to ARM.
Rat embryos with ARM were obtained by treating pregnant rats with administration of ethylenethiourea (ETU). Normal rat embryos and embryos with ARM from gestational days 12.5 to 20 were sectioned serially and sagittally and stained with H & E. The relevant structure including cloaca and urorectal septum (URS) were examined in a temporospatial sequence.
Characteristics of anorectum development in ARM rat embryos treated by ETU were as follows: (1) URS never fused with cloaca membrane. (2) Dorsal cloacal membrane was maldeveloped. (3) Cloacal configuration was abnormal. (4) Tail groove never appeared. All type of ARM was the rectourethal fistula and common cloaca in ETU-treated rat embryos and was discernible on gestation day 16.
Absence of the tail groove and maldevelopment of the dorsal cloacal membrane, cloacal configuration, and urorectal septum are likely to be responsible for the formation of ARM. Failure of fusion of the URS with cloacal membrane is the immediate reason for rectourethral fistula or common cloaca in ETU-treated rats.
肛门直肠畸形（ARM）的胚胎学和病理学方面仍未得到充分理解。目前尚无被普遍接受的理论来解释肛门直肠胚胎学以及导致ARM的异常发育。本研究的目的是观察大鼠肛门直肠的发育过程，并探索导致ARM的异常胚胎发育情况。
通过给怀孕大鼠施用乙硫脲（ETU）来获得患有ARM的大鼠胚胎。将妊娠第12.5天至20天的正常大鼠胚胎和患有ARM的胚胎进行连续矢状切片，并用苏木精和伊红染色。按时间顺序检查包括泄殖腔和尿直肠隔（URS）在内的相关结构。
ETU处理的患有ARM的大鼠胚胎肛门直肠发育特征如下：（1）URS从未与泄殖腔膜融合。（2）背侧泄殖腔膜发育不良。（3）泄殖腔形态异常。（4）尾沟从未出现。在ETU处理的大鼠胚胎中，所有类型的ARM均为直肠尿道瘘和共同泄殖腔，在妊娠第16天即可识别。
尾沟缺失以及背侧泄殖腔膜、泄殖腔形态和尿直肠隔发育不良可能是导致ARM形成的原因。URS与泄殖腔膜融合失败是ETU处理的大鼠出现直肠尿道瘘或共同泄殖腔的直接原因。
